For a biological method, in particular, a method for preparing hydroxy-derivatives of steroids including cholesterol by means of microorganisms, a method by which cholesterol is converted into 25-hydroxycholesterol using microorganisms of the genus Streptomyces has been disclosed in Japanese Laid-Open Patent Publication No. 123997/95. Also, in the biological conversion, which is interesting, of compounds other than steroids, there are known the methods for preparing 25-hydroxyvitamin D compounds by the hydroxylation of vitamin D compounds using microorganisms, for example, Nocardia autotrophica, Streptomyces roseosporus, Amycolata saturnea, Amycolata autotrophica, Sphingomonas sp. (Japanese Laid-Open Patent Publication Nos. 166090/92, 241197/95).
It is known that cholesterol may be, for example, an intermediate on the chemical synthesis of various kinds of vitamin D compounds (Yuki Gosei Kagaku (Organic Synthetwic Chemistry) 37, 809-829 (1979)), and compounds wherein one or more of the specific sites of cholesterol is/are hydroxylated beforehand may be expected for their use as intermediates on the synthesis of various hydroxylated vitamin D compounds. Indeed, according to the conversion method using microorganisms described in the abovementioned Japanese Laid-Open Patent Publication No. 123997/95, it has been published that cholesterol can be selectively hydroxylated at the 25-position which is preferable in relation to activated vitamin D.
However, the hydroxylation efficiency, according to the method described in said patent publication, is not always satisfactory. From the view point of improving the water-solubility of final compounds derived from cholesterol, for example, vitamin D compounds, it would be also desired to provide not only mono-hydroxylated cholesterols but also further hydroxylated cholesterols, for example, dihydroxylated cholesterols.
The purpose of the present invention is therefore to provide a method for efficiently preparing mono-hydroxylated cholesterols, in particular 25-hydroxycholesterol, and a method for preparing further hydroxylated dihydroxycholesterols, and new dihydroxycholesterols per se.